以Ca-M-Al(M=Mg,La,Ce,Y)层状双氢氧化物为前驱体的固体碱用于 酯交换合成碳酸二甲酯

碳酸二甲酯(DMC)是一种环境友好型绿色化学品,可作为甲基化和羰基化试剂用于取代传统剧毒的硫酸二甲酯和光气.另外,DMC具有良好的溶解性能,可用于高级溶剂;DMC分子中具有高的氧含量,可用作汽油添加剂来提高汽油的辛烷值;DMC还可用作聚碳酸酯的原料.随着人们环保意识的不断增强,DMC的生产和应用呈现出巨大的吸引力和市场潜力.DMC合成方法主要有光气法、甲醇氧化羰化法、尿素醇解法及酯交换法等.酯交换法具有反应条件温和、产率高等优点,是目前工业制备DMC的主要方法.研究发现,相对于酸性催化剂,碱性催化剂更有利于酯交换法合成DMC.金属氧化物催化剂具有活性高、热稳定性高及可连续重复回收利用等优点,因而引起了广泛关注.CaO对于酯交换合成DMC反应具有良好的催化活性,但其稳定性差.因此,通常采用复合金属氧化物来促进CaO的分散,并增加金属间相互作用以防止CaO流失.研究发现,经煅烧后的Mg-Al,Ca-Al和Ca-Mg-Al催化剂对于酯交换反应具有高的活性和稳定性.此外,通过碱性稀土金属(La,Ce和Y)的引入可以修饰催化剂上的碱性位点,从而调变催化剂的碱性.本文合成了一系列以Ca-M-Al(M=Mg,La,Ce,Y)层状双氢氧化物为前驱体的固体碱催化剂,将其用于甲醇与碳酸丙烯酯酯交换合成DMC.通过X射线衍射、热重分析、红外光谱、X射线光电子能谱、电感耦合等离子体、CO2程序升温脱附和Hammett指示剂对催化剂进行了表征.研究发现,各催化剂的活性高低依次为:Ca-Y-Al相似文献   

固体碱在二氧化碳-甲醇法合成碳酸二甲酯反应中的作用

本文探讨了固体碱的制备和预处理等因素对于CO₂-甲醇法合成碳酸二甲酯(DMC)的影响,发现微波法所制碱性沸石等多孔材料的反应活性高于浸渍法所制样品。本文首次报道了微波辐射低压合成DMC的新方法,该法能极大地缩短反应时间并提高产物选择性。研究表明:CO₂和甲醇生成DMC的反应在热力学上是几乎不能进行的,加入固体碱的实质是提供了一条耦合的途径。     

过渡金属改性Mg-Al基固体碱催化剂上碳酸丙烯酯与甲醇合成碳酸二甲酯的研究

以共沉淀法制备了一系列不同价态过渡金属(Fe、Cu、Zr)改性的Mg-Al固体碱催化剂,考察了其对于甲醇与碳酸丙烯酯(PC)酯交换合成碳酸二甲酯的反应性能。采用XRD、N₂吸附-脱附、FT-IR、XPS、CO₂-TPD等手段对催化剂的物理化学性质进行了表征。结果表明,催化剂的碱强度、碱密度是影响催化活性的主要因素,不同价态过渡金属的加入可以调控Mg-Al固体催化剂的碱性。在考察的催化剂中,FeMgAl催化剂具有最高的表面碱密度,因此,表现出最好的催化性能。在温度为65℃、时间为4 h、甲醇与PC物质的量比为10∶1、催化剂用量为4%的反应条件下,PC转化率可达66.2%。     

固体碱催化环戊酮和碳酸二甲酯合成己二酸二甲酯

以固体酸碱为催化剂,研究了碳酸二甲酯与环戊酮合成己二酸二甲酯的反应,并考察了反应温度、反应时间、催化剂用量和原料摩尔配比等因素对反应结果的影响．结果表明,固体酸催化剂不利于己二酸二甲酯的生成,而具有中强碱位的MgO对反应具有较好的催化性能．当以MgO为催化剂,在反应温度为260℃,反应时间5h,催化剂用量为反应物质量的1．5％,原料摩尔配比为环戊酮／DMC=1／4的最佳条件下,环戊酮的转化率和己二酸二甲酯的选择性分别达到85．5％和50．9％．同时,反应的主要副产物为环戊酮自身缩合的产物（2．环戊烯基环戊酮）以及环戊酮的甲基化产物（2-甲基环戊酮、2-甲基己二酸二甲酯）等．另外,反应是通过固体碱活化环戊酮的α-H进行,而2-甲氧基羰基环戊酮是生成己二酸二甲酯的中间体．     

固体碱碱性位对丙酮和碳酸二甲酯反应的影响

考察了固体碱不同的碱性位对丙酮和碳酸二甲酯反应的影响,并对反应在不同碱性位上的反应机理进行了推测．实验结果表明,由表面羟基引起的弱碱位有利于丙酮自身缩合反应的进行,主产物为二丙酮醇、4-甲基-3-戊烯-2-酮和4-甲基4-戊烯-2-酮;Lewis酸碱离子对有利于碳酸二甲酯的甲基化反应的发生,主产物为2-甲氧基丙烯;而由固体碱表面配位不饱和的O^2-所造成的强碱位有利于碳酸二甲酯的甲氧基羰基化产物的生成,主产物为乙酰乙酸甲酯;同时发现各种产物的收率与对应的各碱性位的碱量之间均具有较好的线性关系．     

钙铈基催化剂上碳酸丙烯酯和甲醇制备碳酸二甲酯的研究

采用溶胶凝胶法制备了不同比例的钙铈基催化剂,并研究了其对于碳酸丙烯酯和甲醇制备碳酸二甲酯的酯交换反应性能。结果表明,Ca∶Ce=9的催化剂在反应时间2 h,温度40℃,甲醇与碳酸丙烯酯物质的量比为15∶1,催化剂用量为碳酸丙烯酯用量4%的条件下,碳酸丙烯酯转化率达到91.1%,碳酸二甲酯选择性达到91.7%。采用XRD、N2吸附-脱附、FT-IR、XPS和CO₂-TPD对催化剂进行了表征。结果表明,催化剂表面的氧空穴越多,中等碱性位数量越多,越有利于甲醇的活化,催化剂的活性越好。     

固体碱在二氧化碳-甲醇法合成碳酸二甲酯反应中的作用

本文探讨了固体碱的制备和预处理等因素对于ＣＯ_２~－甲醇法合成碳酸二甲酯（ＤＭＣ）的影响,发现微波法所制碱性沸石等多孔材料的反应活性高于浸渍法所制样品。本文首次报道了微波辐射低压合成ＤＭＣ的新方法,该法能极大地缩短反应时间并提高产物选择性。研究表明： ＣＯ_２和甲醇生成 ＤＭＣ的反应在热力学上是几乎不能进行的,加入固体碱的实质是提供了一条耦合的途径。     

非晶态铁基固体碱催化剂的酯交换性能

通过化学还原法和共沉淀法分别制备了非晶态和晶态的FeCeOx/SiO2固体碱催化剂。与晶态的FeCeOx/SiO2相比,非晶态的FeCeOx/SiO2催化剂对梨醇酯与甲醇的酯交换活性显著提高。通过电感耦合等离子体质谱(ICP-MS)、N2吸附-脱附、透射电子显微镜(TEM)结合选区电子衍射(SAED)、X射线衍射(XRD)、X射线光电子能谱(XPS)、CO2-TPD和NH3-TPD等对催化剂进行表征。结果表明催化剂的活性与其碱性密切相关,非晶态FeCeOx/SiO2显示出相对于晶态FeCeOx/SiO2更强的碱性。使用非晶态FeCeOx/SiO2催化剂进行梨醇酯酯交换反应,在130℃下反应10 h,梨醇酯的转化率达到95%,异戊烯醇的选择性达到96%。在重复使用10次后,催化剂活性基本不变。对新鲜的和套用10次后的FeCeOx/SiO2催化剂进行X射线衍射分析,表明该催化剂在套用10次后仍未晶化,证实其具有良好的稳定性,说明该催化剂在非均相催化酯交换反应中具有应用价值。     

高稳定性CaO-ZrO2固体碱催化剂的表征和催化性能

用共沉淀法经高温焙烧制备了CaO摩尔分数从10%至50%的CaO-ZrO₂系列催化剂, 将其应用于碳酸丙烯酯和甲醇酯交换合成碳酸二甲酯过程, 并通过XRD, FT-IR, BET, ICP, CO₂-TPD, XPS等表征手段研究了催化剂的物性及其催化性能随组成变化的的规律. 结果表明, 当CaO摩尔分数高于30%时, 表面出现游离的CaO, 虽然具有强碱性和高活性, 但是稳定性差; 而当CaO摩尔分数低于30%时, Ca^2＋进入ZrO₂晶格, CaO与ZrO₂形成连续固溶体, 并且随着CaO含量的增加, 晶格氧的电荷密度增加, 催化剂的碱性增强, 使得CaO-ZrO₂催化剂在碳酸丙烯酯和甲醇酯交换合成碳酸二甲酯过程中获得了高活性和高稳定性.     

高稳定性CaO-ZrO2固体碱催化剂的表征和催化性能

用共沉淀法经高温焙烧制备了CaO摩尔分数从10%至50%的CaO-ZrO₂系列催化剂, 将其应用于碳酸丙烯酯和甲醇酯交换合成碳酸二甲酯过程, 并通过XRD, FT-IR, BET, ICP, CO₂-TPD, XPS等表征手段研究了催化剂的物性及其催化性能随组成变化的的规律. 结果表明, 当CaO摩尔分数高于30%时, 表面出现游离的CaO, 虽然具有强碱性和高活性, 但是稳定性差; 而当CaO摩尔分数低于30%时, Ca^2＋进入ZrO₂晶格, CaO与ZrO₂形成连续固溶体, 并且随着CaO含量的增加, 晶格氧的电荷密度增加, 催化剂的碱性增强, 使得CaO-ZrO₂催化剂在碳酸丙烯酯和甲醇酯交换合成碳酸二甲酯过程中获得了高活性和高稳定性.     

Synthesis of dimethyl adipate from cyclopentanone and dimethyl carbonate over solid base catalysts

A facile route for the synthesis of dimethyl adipate (DAP) from cyclopentanone and dimethyl carbonate (DMC) in the presence of solid base catalysts has been developed.It was found that the intermediate carbomethoxycyclopentanone (CMCP) was produced from cyclopentanone with DMC in the first step,and then CMCP was further converted to DAP by reacting with a methoxide group.The role of the basic catalysts can be mainly ascribed to the activation of cyclopentanone via the abstraction of a proton in the α-position by base sites,and solid bases with moderate strength,such as MgO,favor the formation of DAP.     

NiCu bimetallic catalysts derived from layered double hydroxides for hydroconversion of n-heptane

Supported Ni Cu bimetallic catalysts have been produced in-situ on commercial Al₂O₃ by using layered double hydroxides as precursors. The resulting catalysts show a uniform Ni and Cu distribution, thus providing good activity and selectivity in the reforming reaction of n-heptane. The catalytic performance has been found to depend on the Cu/Ni ratio, revealing the synergic catalysis between homogeneously dispersed Ni and Cu sites. The good catalysis of Ni Cu bimetallic cata...     

Synthesis of dimethyl carbonate and propylene glycol from transesterification of propylene carbonate and methanol using quaternary ammonium salt catalysts

Summary The synthesis of dimethyl carbonate (DMC) was investigated through the transesterification of propylene carbonate (PC) with methanol using quaternary ammonium salt catalysts. The reaction was carried out in an autoclave at 120-140 oC under carbon dioxide pressure of 250-400 psig. The main by-product was propylene glycol. The quaternary salts of larger alkyl group and more nucleophilic counter anion exhibited higher catalytic activity. Kinetic studies were also performed to better understand the reaction mechanism. Quaternary ammonium chlorides immobilized on polystyrene supports were also tested for their possible uses as heterogeneous catalysts.     

The formation of acrylonitrile over solid base catalysts

The reaction of methanol and acetonitrile to form acrylonitrile has been studied over solid base catalysts derived from MgO. High surface area MgO produced the best yields of acrylonitrile and propionitrile, but higher specific activity was achieved by impregnating the MgO support with chromium oxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Promotion of Ionic Liquid to Dimethyl Carbonate Synthesis from Methanol and Carbcn Dioxide

Promotion of ionic liquid, 1-ethyl-3-methylimidazolium bromide (emimBr), to the synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide in the presence of potassium carbonate and less amount of methyl iodide under mild conditions was investigated. The results showed that the high selectivity and raised yield of DMC was achieved due to the addition of emimBr in the reaction system. And effect of several reaction conditions such as temperature, pressure and amount of emimBr was discussed.     

双功能催化剂中不同组分对一步法合成二甲醚的影响

采用干磨法,选用不同种类甲醇合成组分和不同种类的甲醇脱水组分制备双功能催化剂,并在高压固定床反应器评价其催化性能.研究表明,催化剂JC207是一种较优的甲醇合成催化剂,其最佳配比为80％.分子筛是一种较好的甲醇脱水催化剂,其最佳配比为20％.通过寿命试验和催化剂的XRD表征发现催化剂晶相没有改变,催化剂结构保持稳定.     

Synthesis of polycarbonate from dimethyl carbonate and bisphenol-a through a non-phosgene process

A novel nonphosgene process for producing bisphenol-A polycarbonate (PC) was developed through a transesterification between bisphenol-A (BPA) and dimethyl carbonate (DMC) and a melt-polycondensation of the resulting bisphenol-A bismethylcarbonate (1). The transesterification was carried out by heating bisphenol A in dimethylcarbonate in the presence of Lewis acid catalysts, removing the by-producing methanol using molecular shieves 4A. Among various catalysts, a combination of (Bu₂SnCl)₂O and dimethylaminopyridine gave the best results to produce 1 in 22% yield for 48 h. Using a larger amount of the molecular sieves further improved the yield to 80% in 120 h. The resulting 1 was heated under reduced pressure in the presence of titanium catalysts to produce PC in good yields. The resulting PC had high weight average molecular weight (M_w) of 75,000. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2087–2093, 1999     

Microwave-treated layered double hydroxides containing Ni and Al: The effect of added Zn

Ni containing layered double hydroxides (LDHs) have been prepared by precipitation and hydrothermally treated under microwave irradiation for different periods of time. The solids have been calcined at three temperatures corresponding to stable phases formed during thermal decomposition of LDHs. The properties of the irradiated samples and of the calcined products were studied in order to ascertain whether the ageing treatment under microwave irradiation modifies not only the properties of the layered materials, but also the properties of the calcined products. A structural and textural study was carried out by PXRD, FT-IR and Vis-UV spectroscopy, thermal analyses (DTA and TG), N₂ adsorption/desorption at −196 °C and TEM microscopy; the reducibility of the nickel species was studied as well by TPR. The results show that the microwave treatment leads to better crystallized LDHs with modified thermal stability and reducibility. In addition, the degree of crystallinity of the layered precursors and their textural properties determine the properties of their thermal decomposition products.     

杂多阴离子柱撑水滑石的合成、热稳定性、酸碱性研究

采用水溶液中阴离子直接交换法合成了过渡金属单取代Keggin结构杂多阴离子SiW11M(H2O)O39^6^- (M=Mn^2^+, Fe^2^+, Co^2^+, Ni^2^+, Cu^2^+,Zn^2^+)柱撑水滑石。用元素分析、XRD和IR对产物的组成与结构进行了表征。XRD结果给出柱撑产物的底面间距达1.47nm。DTA结合不同温度下焙烧样品的XRD、IR研究表明, 柱撑水滑石在低于250℃时脱除物理吸附水和层间水; 在400~500℃之间脱除层上羟基, 形成一个无定形的混合氧化物状态; 在600℃以上无定形态结晶为晶态氧化物混合物。异丙醇探针反应表明, 柱撑水滑石具有高于水滑石前驱体和相应杂多酸盐的催化活性, 且同时存在酸碱两类催化活性中心, 但酸中心明显较强。